Community structure dynamics and carbon stock change of rehabilitated mangrove forests in Sulawesi, Indonesia

To date, discourse associated with the potential application of “blue carbon” within real‐world carbon markets has focused on blue carbon as a mitigation strategy in the context of avoided deforestation (e.g., REDD+). Here, we report structural dynamics and carbon storage gains from mangrove sites that have undergone rehabilitation to ascertain whether reforestation can complement conservation activities and warrant project investment. Replicated sites at two locations with contrasting geomorphic conditions were selected, Tiwoho and Tanakeke on the island of Sulawesi, Indonesia. These locations are representative of high (Tiwoho, deep muds and silty substrates) and low (Tanakeke, shallow, coralline sands) productivity mangrove ecosystems. They share a similar management history of clearing and conversion for aquaculture before restorative activities were undertaken using the practice of Ecological Mangrove Rehabilitation (EMR). Species diversity and mean biomass carbon storage gains after 10 yr of regrowth from the high productivity sites of Tiwoho (49.2 ± 9.1 Mg C·ha？1·yr？1) are already almost of one‐third of mean biomass stocks exhibited by mature forests (167.8 ± 30.3 Mg C·ha？1·yr？1). Tiwoho's EMR sites, on average, will have offset all biomass C that was initially lost through conversion within the next 11 yr, a finding in marked contrast to the minimal carbon gains observed on the low productivity, low diversity, coral atoll EMR sites of Tanakeke (1.1 ± 0.4 Mg C·ha？1·yr？1). These findings highlight the importance of geomorphic and biophysical site selection if the primary purpose of EMR is intended to maximize carbon sequestration gains. Mangroves are highly productive habitats and provide a vast range of critically important ecosystem services (Lau 2013) that support the livelihoods and wellbeing of hundreds of millions of coastal people across the tropics. Of these ecosystem services, perhaps the most discussed in recent international discourse is the significant role that mangroves and other “blue carbon” habitats such as seagrass beds and tidal saltmarshes can play in climate change mitigation and adaptation through counterbalancing anthropogenic CO2 emissions. Despite their importance, mangroves are undergoing substantial declines in extent, habitat quality, and intactness through a range of land use, land use change, and forestry (LULUCF) drivers, including the conversion of mangroves to agriculture and aquaculture ponds (Richards and Friess 2016, Thomas et al. 2017). Aquaculture expansion in Southeast Asia requires the clearing of mangroves